The trucking industry has for many years used tractor/trailer combinations to transport cargo over roadways. The tractor and the trailer are mechanically coupled together so that the tractor can pull the trailer loaded with cargo in an efficient and cost effective manner. Pneumatic and electrical links between the tractor and the trailer provide a trailer brake system with power and control signals for system operation.
Heavy vehicle pneumatic brake systems use compressed air for all three major braking functions, i.e., parking, service or normal, and emergency. As such, compressed air is constantly used and regenerated in operation of the heavy vehicle. Trailer air brake systems include brake assemblies, brake chambers, and an air reservoir, among other components. The brake assemblies are coupled to the trailer wheels. The brake chambers are coupled to the brake assemblies for selectively engaging and disengaging the brake assemblies to stop and/or prevent rotation of the trailer wheels. The reservoir stores air under pressure provided by the tractor via the pneumatic links. The air under pressure is selectively provided to the brake chambers.
A compressor is used to generate a system tank pressure of 110 psi to 120 psi for supplying the system lines. In most systems, air from the compressor passes through various reservoirs, check valves and safety vales prior to use in a brake chamber located adjacent to an axle. In the field relating to antilock braking systems (hereinafter “ABS”), a modulator valve is situated between a source of air pressure and the brake chamber or actuator. Conventionally, modulators are solenoid operated on/off air valves that are controlled by a system controller. The controller selectively opens and closes the modulator valves to control air flow. Typically, a modulator includes two separate control circuits using solenoids, one for building pressure in the brake chambers and one for exhausting pressurized air from the brake chambers. Modulators are also used in parking and emergency braking functions. In addition to braking systems, solenoid valves are also used in other vehicle pneumatic systems, such as seats, doors and suspensions for example.
Many ABS modulators are known in the art. One exemplary modulator uses essentially high capacity, on/off air valves that incorporate a pair of electrical solenoids for control. The solenoids provide the electro-pneumatic interface or link between the brake controller electronics and the air brake system. The modulator may include a normally open exhaust solenoid and a normally closed supply solenoid, an inlet diaphragm valve and an exhaust diaphragm valve. When a solenoid is energized it either opens or closes thereby causing the exhaust or re-application of air pressure to the brake actuator.
If an antilock event is sensed in an ABS, an electronic control unit sends suitable signals to a solenoid valve assembly (usually a pair of solenoid valves) associated with the modulator. The solenoid valves provide an electro-pneumatic interface between the electronic controller and the air brake system. The antilock controller immediately begins to modify brake application using the modulator to control the impending locked wheel. The coils associated with the respective solenoid valves are energized or de-energized in a predetermined sequence by the controller. As is known in the art, when a solenoid coil is energized, a core or shuttle is moved to either open or close an associated air passage. This movement either opens or closes the exhaust passage or reapplies air pressure to the brake actuator. Each of the solenoid valves is independently controlled by the electronic control unit. By opening and closing the solenoid valves, the antilock controller simulates brake “pumping” at substantially beyond any rate a driver could physically pump the brakes to avoid skidding.
Seal performance and integrity over the operational life of a modulator solenoid valve is highly desired in the industry. In an ABS equipped heavy vehicle, the solenoid valve may be opened and closed up to 5 million times in the forecasted life of the valve. The industry standard permissible leakage rate for valves in the closed position is 2.5 cc/min. The life usage expectancy of a parking modulator solenoid valve is considerably less, i.e., 200.000 cycles. Nevertheless, the seal integrity in a parking system is also desirable. When a truck is parked overnight, an ineffective seal can permit a tank to be undesirably drained of compressed air. This situation requires compulsory compressor use to recharge the tank the following morning prior to use of the heavy duty vehicle. Any loss of operation time of the vehicle may contribute to reduced profits for the trucking company. Seal integrity is important in other pneumatic non-brake systems as well.
The present invention provides a new and improved solenoid valve having an integrated spherical soft seal and offering improved sealing performance, simplified machining requirements and reduced manufacturing costs. The valve features an integrated armature assembly having a biased spring and ball seal. The design eliminates the need for an additional guide member for aligning the armature or a specially molded valve seat insert. Further, the present invention advantageously creates and maintains a seal when the ball seal and valve seat are axially misaligned.